Segmented seal assembly

ABSTRACT

A light weight seal assembly divided into arcuate segments surrounds the tips of an annular row of rotating blades of an axial flow gas turbine. Each segment comprises formed sheet metal members brazed together and attached to the blade ring in the turbine casing. Leakage through expansion gaps between segments is prevented by sealing strips which bridge the gaps. Heat is transferred from the light weight seal structure into the relatively massive blade ring which is cooled by an external air supply. A soft wearable liner is brazed to the inside of the segment to insulate against heat transfer from the gas stream into the blade ring.

llniled Males Patent Ralraim et al.

[15] 3,656,062 51 Apr. 10,1972

SEGMENTED SlEAl, ASfilEMBlLY Westinghouse Electric Corporation,Pittsburgh, Pa.

Filed: July 2, 1970 Appl. No.: 51,970

[73] Assignee:

US. Cl ..415/l71,4l5/174,415/217 rm. CI ..1F0ld1l/08,F04d 29/08References Cited UNITED STATES PATENTS Field ofSearch ..415/174, 171,136, 199, 1193,.

3,314,648 4/1967 Howald ..415/1 74 FOREIGN PATENTS OR APPLICATIONS611,004 12/1960 Canada ..4l5/l36 1,020,900 2/1966 GreatBritain ..4l5/174Primary Exqminer-Henry F. Raduazo Attorney-A. T. Stratton, F. P. Lyleand F. Cristiano, Jr.

[57] ABSTRACT A light weight seal assembly divided into arcuate segmentssurrounds the tips of an annular row of rotating blades of an axialflowgas turbine. Each segment comprises formed sheet metal membersbrazed together and attached to the blade ring in the turbine casing.Leakage through expansion gaps between segments is prevented by sealingstrips which bridge the gaps. Heat is transferred from the light weightseal structure into the relatively massive blade ring which is cooled byan external air supply. A soft wearable liner is brazed to the inside ofthe segment to insulate against heat transfer from the gas stream intothe blade ring.

5 Claims, 4 Drawing Figures PATENTEDAPR 18 ran 3, 656,862

- WITNESSES 4 INVENTORS SEGMENTIED SEAL ASSIEWILY BACKGROUND OF THEINVENTION This invention relates, generally, to elastic fluid machinesand, more particularly, to a segmented seal assembly for axial flow gasturbines.

In order to maintain high first stage efficiency, static seal structureshave been provided to minimize by-pass leakage of the motive fluidaround the first stage stator vanes of an axial flow gas turbine. Inorder to improve the efficiency of any other stage of an axial flowturbine, it is desirable to decrease leakage of the motive fluid pastthe tips of the rotor blades for that stage. This is accomplished byreducing the tip clearance by providing a light weight segmented annularseal assembly around the rotor blades.

SUMMARY OF THE INVENTION In accordance with one embodiment of theinvention, an

annular seal assembly divided into a plurality of arcuate segmentssurrounds a row of rotating blades of an axial flow turbine. Eachsegment comprises an axially extending member and a radially extendingmember of formed sheet metalbrazed together and attached to the bladering in the stator casing of the turbine. A honeycombed liner composedof a relatively soft wearable material is secured on the inner surfaceof each segment to insulate against heat transfer from the motive fluidinto the blade ring. Leakage through expansion gaps between segments isprevented by sealing strips which bridge the gaps. Heat is transferredfrom the light weight seal structure into the relatively massive bladering which is cooled by an external air supply.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of thenature of the invention, reference may be had to the following detaileddescription, taken in conjunction with the accompanying drawing, inwhich:

FIG. 1 is a view, partly in axial section and partly in elevation, of aportion of an axial flow gas turbine with a segmented seal assemblyconstructed in accordance with principles of the present invention;

FIG. 2 is an isometric view of one arcuate segment of the seal assembly;

FIG. 3 is a view, in elevation taken along line IIIIII in FIG. 1,showing an expansion gap between adjacent seal segments; and

FIG. 4 is a view, similar to FIG. 1, of a modified seal assembly.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings,particularly to FIG. 1, the structure shown therein comprises a portionof an axial flow gas turbine 10 which includes an annular array ofcircumferentially spaced stationary blades or vanes 11 secured betweenarcuate outer shroud segments 12 and arcuate inner shroud segments (notshown). The outer shroud segments 12 are mounted in a stator blade ring13 disposed inside a turbine casing (not shown) which is generallycircular in cross section.

An annular row of rotor blades 14 is disposed immediately downstreamfrom the stationary vanes 11. The rotor blades 14 are suitably attachedto the periphery of a rotor wheel (not shown) secured to a shaft (notshown) rotatably mounted in the turbine casing in a manner well known inthe art. In the arrangement shown in FIG. 1, the stationary blades 11and the rotor blades 14 constitute the last stage of the turbine whichincludes other stationary and rotary blades disposed upstream from theblades 14, thereby providing a multi-stage turbine.

A hot motive gas is supplied to the turbine from suitable combustionchambers (not shown). The hot motive gas flows from the combustionchambers through the stationary vanes and the rotating blades, therebydriving the turbine shaft by energy extracted from the hot motive fluidin a manner well known in the art.

In order to minimize the leakage of the motive fluid around the rotatingblades 14, an annular seal assembly 2l surrounds the row of rotatingblades 14$. The seal assembly 21 is divided into a plurality of arcuatesegments 22 which are disposed end-to-end around the rotating blades 14.The segments 22 are supported by the blade ring 13 in a manner whichwill be described more fully hereinafter.

As shown more clearly in FIGS. 2 and 3, each segment 22 comprises agenerally axially disposed member 23 and a radially disposed member 2Awhich are preferably formed from relatively lightweight sheet metal andbrazed together. An angularly disposed brace member 25, also formed fromsheet metal, may be secured to the members 23 and 24 to maintain themembers in the desired angular relation.

Expansion gaps 26 are provided between adjacent segments to permitcircumferential expansion due to heating of the segments. Leakagethrough the expansion gaps is prevented by sealing strips 27 whichbridge the gaps between the members 23. Sealing strips 28 bridge thegaps between the radially extending members 24. The strips 27 and 26 maybe secured to the members 23 and 24, respectively, as by brazing.

A honeycombed soft wearable liner 30 is secured to the inside of eacharcuate member 23. The liner 30 is preferably composed of a metal whichis softer than the metal of which the blades 14 are composed, therebypermitting the liner to wear away if it is rubbed by the rotatingblades. In this manner the turbine may be constructed with relativelysmall cold tip clearance between the tips of the blades and the linerwhich provides a more eflicient stage and more horsepower output fromthe turbine. The wearable material, which is secured to the member 23,as by brazing, will wear clear if rubbing occurs, thus permittingminimum possible tip clearance.

Furthermore, the honeycomb material insulates against heat transfer fromthe gas stream into the blade ring, thereby increasing the efiiciency ofthe turbine. Heat is transferred from the light weight seal structureinto the relatively massive blade ring to reduce expansion of the sealmembers. The blade ring 113 may be cooled by an external cool air supplyin a manner known in the art, for example as disclosed in US. Pat. No.3,427,000, issued Feb. II, 1969, to A. J. Scalzo and assigned toWestinghouse Electric Corporation, to decrease expansion of the bladering during transient conditions.

By way of example, the annular seal assembly 21 may consist of 36segments 22. The radially extending member 24 of each segment may beattached to a radially extending face 31 on the end of the blade ring 13by means of a bolt 32 which is threaded into the blade ring 13. Anopening 33 is provided in the brace member 25 to permit access to thehead of the bolt 32.

Another advantage of the seal arrangement shown in FIG. I is thatseveral inches of material have been removed from the rear end of theblade ring 113 as shown by the dot-dash line 34 which shows the priorcontour of the blade ring. The removal of this material results in alighter and less costly blade ring.

As explained hereinbefore, the seal mounting arrangement shown in FIG. Iis suitable for use with the last stage of a multistage turbine. Theseal mounting arrangement shown in FIG. 4 is suitable for use with anintermediate stage of a multistage turbine. As shown in FIG. 4, anannular recess 35 is provided in the blade ring 13 to provide a radiallyextending face 31a on the blade ring to which the radially extendingmember 24 of each seal segment 22 is attached by means of a bolt 32. Inthis manner the annular seal assembly may be utilized with anintermediate stage of the turbine without interferring with the mountingof the stationary vanes in the blade ring of the turbine.

A seal ring 36 is retained in position by an outwardly extendingextension 37 on the member 23 to prevent leakage through the jointbetween members 12 and 13. The ring 36 may be an On'ng divided intoseveral sections. Thus, the annular seal assembly may be utilized withthe rotary blades of an intermediate stage as well as with the rotaryblades of the last stage of a multi-stage turbine.

From the foregoing description, it is apparent that the inventionprovides a light weight seal assembly for use with the rotating bladesof a turbine which makes it possible to maintain minimum tip clearancefor the blades, thereby reducing leakage of the motive fluid around theturbine blades and increasing the efiiciency of the turbine. Heat istransferred from the light weight seal structure into the relativelymassive blade ring which supports the seal structure. Also, heat lossesfrom the hot motive fluid are reduced by the honeycombed structure ofthe wearable liner utilized in the seal assembly.

We claim:

1. In an axial flow turbine, in combination,

a relatively massive stator blade ring having an annular array ofstationary vanes mounted therein,

an annular row of metal rotor blades disposed immediately downstreamfrom the stationary vanes,

an annular seal assembly divided into a plurality of arcuate segmentssurrounding the row of rotor blades,

each segment comprising a generally axially disposed member and aradially disposed member secured together,

an angularly disposed brace member secured to said axially and radiallydisposed members,

said segments being spaced circumferentially to provide expansion gapsbetween segments, and having sealing strips bridging said gaps,

said blade ring having a radially disposed face thereon, and

threaded screw means attaching the radially disposed members to saidface.

2. The combination defined in claim 1 wherein said members are fonned ofsheet metal and are of relatively lighter construction than said bladering.

3. The combination defined in claim 2, including a liner composed of arelatively soft wearable material secured on the inner surface of theaxially disposed member.

4. The combination defined in claim 1 wherein the rotor blades are inthe last stage of a multi-stage turbine,

the radial face is on the end of the blade ring, and the seal assemblyextends axially from the blade ring face in a cantilever fashion.

5. The combination defined in claim 1, wherein the rotor blades are inan intermediate stage of a multi-stage turbine,

the blade ring has a second annular array of stationary vanes mountedthereto and forming a part of a succeeding stage,

the blade ring has an annular recess between said arrays of vanesproviding said face,

the axially disposed member has an outwardly extending extensionthcreon, and

a seal ring retained in sealing position by said extension.

1. In an axial flow turbine, in combination, a relatively massive statorblade ring having an annular array of stationary vanes mounted therein,an annular row of metal rotor blades disposed immediately downstreamfrom the stationary vanes, an annular seal assembly divided into aplurality of arcuate segments surrounding the row of rotor blades, eachsegment comprising a generally axially disposed member and a radiallydisposed member secured together, an angularly disposed brace membersecured to said axially and radially disposed members, said segmentsbeing spaced circumferentially to provide expansion gaps betweensegments, and having sealing strips bridging said gaps, said blade ringhaving a radially disposed face thereon, and threaded screw meansattaching the radially disposed members to said face.
 2. The combinationdefined in claim 1 wherein said members are formed of sheet metal andare of relatively lighter construction than said blade ring.
 3. Thecombination defined in claim 2, including a liner composed of arelatively soft wearable material secured on the inner surface of theaxially disposed member.
 4. The combination defined in claim 1 whereinthe rotor blades are in the last stage of a multi-stage turbine, theradial face is on the end of the blade ring, and the seal assemblyextends axially from the blade ring face in a cantilever fashion.
 5. Thecombination defined in claim 1, wherein the rotor blades are in anintermediate stage of a multi-stage turbine, the blade ring has a secondannular array of stationary vanes mounted thereto and forming a part ofa succeeding stage, the blade ring has an annular recess between saidarrays of vanes providing said face, the axially disposed member has anoutwardly extending extension thereon, and a seal ring retained insealing position by said extension.